3,6-Dichloro-2-methoxybenzoic acid (also known by its common name dicamba) is a highly effective and commercially important herbicide that is useful for controlling a wide variety of unwanted vegetation, including agricultural weeds. Convenient and economical methods of preparing dicamba, therefore, are of significant commercial importance.
A number of synthetic routes for the preparation of dicamba have been reported in the literature. One such route generally involves the conversion of 2,5-dichloroaniline to dicamba as shown in Scheme 1 below:
See, e.g., U.S. Pat. No. 4,161,611.
This route, however, typically requires certain process conditions (such as fine milling of the 2,5-dichloroanaline starting material, use of a large excess of sulfuric acid and/or concentrated sulfuric acid in the diazotizing step, etc.) in order to achieve an acceptable conversion of the 2,5-dichloroanaline to the 2,5-dichlorophenol on a commercial scale. The present disclosure provides improved processes that reduce or eliminate the need for such process conditions while still maintaining, or even improving, conversion of the 2,5-dichloroanaline to the 2,5-dichlorophenol.